VICTORIA’S FOREST FRAGMENTATION CONDITION

Abstract

Natural processes, for example fires and storms, climate change, and human activity such as roading, logging and agriculture, divide forested areas into smaller pieces of forest. This process is known as fragmentation. Fragmentation poses direct threats to biodiversity, through limiting the area of forest available to forest reliant species and isolating small populations of fauna and flora, where gaps between fragments are too large to be crossed regularly. The size of gap that can be crossed is dependent on individual species but may be as small as a forest road. To understand the current condition of Victorian forest fragmentation, an analysis based on Ritters et al (2000) has been undertaken.

A forest fragmentation spatial dataset was created using Victoria’s forest extent raster dataset, developed for the Victorian Forest Monitoring program, using a GRASS open source GIS environment. The process calculates the proportion of forested pixels and the conditional probability of any given forested pixel, classifies them into ‘Patch’, ‘Transitional’, ‘Edge’, ‘Perforated’ and ‘Interior’. Fragmentation datasets were later combined with Victorian corporate spatial datasets e.g. IBRA bioregion, public land (PLM 25) etc for further analysis.

The result estimates the proportion of public land forest in each fragmentation category by tenure and bioregion. Fragmentation analysis for the 2009 and 2013 base line years shows a trend of positive improvement in some of the bioregions e.g. Australian Alps, South East Coastal Plain, Riverina and NSW South Western Slopes, which mostly represents recovery and regrowth from fires last decade. The increase of forest interior and decrease of ‘patch’, ‘transitional’, ‘edge’ and ‘perforated’ landscape represents large contiguous forested areas suitable for diverse habitat. Data are currently unavailable for the other bioregions and cross tenure comparisons but will be developed in the future.

Policy impact:
When forest is disturbed, forest interior decreases and other fragmentation categories are increased, leading to threats to biodiversity. Fragmentation analysis measures forest cover and spatial configuration, leading to measures of fragmentation in Victoria’s forest. In turn, we can assess fragmentation’s likely impacts on forest dependent species. Determining trends and locations of particularly fragmented areas will enable policymakers and land managers to target those areas particularly in need of protection or restoration, enabling more effective use of available resources, and enable more effective placement and protection of linking corridors.

Research Findings:
Through remote sensing data and computing and software technologies, we are now able to calculate forest fragmentation in finer spatial scale, allowing us to discover how well our forests are maintaining their integrity. Our study identifies significant improvement in several forest fragmentation categories in a selection of bioregions. Increase of forest ‘interior’ and decrease of ‘patch’ and edge pixels represent recovery and regrowth from the landscape scale fires of last decade.

KEYWORDS:
Forest Fragmentation, biodiversity, Habitat, GIS